1. Field of the Invention
The present invention relates to a method of controlling an ion implantation apparatus.
2. Description of the Background Art
Heretofore, as an ion implantation apparatus, there has been known one type which comprises a mass separation magnet for sorting out and outputting ions having a specific mass number and valence from an ion beam extracted from an ion source, an acceleration tube for accelerating or decelerating the ion beam output from the mass separation magnet, and an energy separation magnet for sorting out and outputting ions having a specific energy from the ion beam output from the acceleration tube, as disclosed, for example, in Patent Document 1.
In this type of ion implantation apparatus, a curvature radius of the ion beam in the energy separation magnet is calculated based on a value of magnetic flux density in the energy separation magnet at each checkup timing before and during ion implantation into a target, a mass number and valence of ion at the checkup timing and a total applied voltage to the ion beam, and it is checked whether the calculated curvature radius falls within a predetermined allowable range with respect to a reference value. This approach is intended to properly detect abnormality in ion species and energy of the ion beam, in the above manner.
However, in the above abnormality detection method, the Patent Document 1 makes no mention of abnormality caused by discharge of an extraction electrode to which an extraction voltage is applied to extract an ion beam from the ion source. In cases where a plurality of types of ions are generated in the ion source, discharge occurring in the extraction electrode gives rise to a problem that an ion beam containing the plurality of types of ions will reach a target, and ions having a mass and energy other than desired values (i.e., non-desired ions) will be implanted into the target.